FIG. 12 is a cross-sectional view showing a printed circuit board relating to a conventional technique.
A printed circuit board 100 relating to the conventional technique includes a base member 112. On a circuit surface of the base member 112, a large number of part assembling conductor layers 114, wiring conductor layers 116 and circuit surface resist layers 118 are formed. On a heat-radiating surface of the base member 112, a solder resist layer 122 is formed so as to cover a large number of heat-radiating conductor layers 120.
Therefore, the printed circuit board 100 relating to the conventional technique has a configuration in which the heat-radiating conductor layers 120 are not exposed, but covered with the solder resist layer 122.
FIG. 13 is a flow chart for explaining manufacturing processes of a printed circuit board relating to the conventional technique. In the flow chart, an A-surface is a circuit surface and a B-surface is a heat-radiating surface.
FIG. 14 to FIG. 21 are process cross-sectional views for explaining manufacturing processes of the printed circuit board relating to the conventional technique.
Referring to FIG. 13 and FIG. 14 to FIG. 21, the following description will discuss the manufacturing processes thereof.
In the first step S101 shown in FIG. 13, as shown in FIG. 14, a base substrate 200 in which metal layers 220 are formed on two surfaces of the base member 112 is prepared as a base member.
In step S102 and step S103, as shown in FIG. 15, after pretreatments such as washing, roughening process and the like, a heat-radiating surface pattern printing process is carried out on the metal layer 220 on the heat-radiating surface side of the base substrate 200 by using an etching resist ink, and the etching resist ink is then cured so that an etching resist layer 320 is formed.
In step S104, as shown in FIG. 16, a circuit surface pattern printing process is carried out on the metal layer 220 on the circuit surface side of the base substrate 200 by using an etching resist ink, and the etching resist ink is then cured so that an etching resist layer 420 is formed.
In step S105, as shown in FIG. 17, an etching process is carried out on the metal layers 220 on the two surfaces of the base substrate 200 so that unnecessary portions are removed.
In step S106, as shown in FIG. 18, ink removing works are carried out so that both of the etching resist layers 320 and 420 on the circuit surface and the heat-radiating surface are removed.
In step S107 and step S108, as shown in FIG. 19, after pretreatments, a first circuit surface resist printing process is carried out on the circuit surface side by using a solder resist ink, and thereafter, by curing the solder resist ink, a first solder resist layer 118a is formed.
In step S109, as shown in FIG. 20, on the first solder resist layer 118a, a second circuit surface resist printing process or letter printing process is carried out by using a solder resist ink, and thereafter, by curing the solder resist ink, a second solder resist layer 118b is formed.
In step S110, as shown in FIG. 21, on the heat-radiating surface side, a heat-radiating surface resist printing process is carried out by using a solder resist ink, and thereafter, by curing the solder resist ink, a solder resist layer 122 is formed.
In step S111 and step S112 of the manufacturing process of the printed circuit board relating to the conventional technique, external shaping and boring processes are carried out, and a surface finishing process is then carried out. The purpose of the surface finishing process is to clean a copper foil surface, and degreasing and rust-removing processes are carried out by using acid.
The above-mentioned printed circuit board and manufacturing method thereof have been described in Japanese Patent Application Laid Open No. 2011-222962 (Patent Document 1) and Japanese Patent Application Laid Open No. H5-267829 (Patent Document 2).